Pressure sensor and process of manufacturing same

ABSTRACT

A pressure sensor includes an evaluation unit and a sensor assembly, which includes a sensor and an electrode arrangement. The sensor generates signals under the action of a pressure profile, and the electrode arrangement transmits the signals to the evaluation unit, which includes an evaluation unit housing, an electric circuit board and a reinforcement element, which is arranged in a radial plane between the electric circuit board and the evaluation unit housing. The reinforcement element is mechanically connected to the electric circuit board and dampens mechanical resonance vibrations of the electric circuit board that occur in the radial plane.

FIELD OF THE INVENTION

The invention relates to pressure sensors that include a sensor and anevaluation unit connected to the sensor by an electrode arrangement andto a process of manufacturing such pressure sensors.

BACKGROUND

Piezoelectric pressure sensors are known and are widely used. Thus, theyare used in pressure indexing of internal combustion engines to detect acylinder pressure prevailing in a pressure chamber as a function of thecrankshaft position or a time. Internal combustion engines includefour-stroke engines and two-stroke engines such as gasoline engines,diesel engines, Wankel engines, etc. In marine diesel engines, they areused for long-term monitoring of a cylinder pressure. Piezoelectricpressure sensors are used to monitor fast pressure profiles that usuallyare in the range of 150 to 250 bar but including pressure peaks of 500bar and higher if pre-ignition and engine knocking occur. However,piezoelectric pressure sensors also can be used in pressure monitoringin jet engines, gas turbines, steam turbines, steam engines, etc.

U.S. Pat. No. 3,364,368, which is hereby incorporated herein by thisreference for all purposes, discloses one such piezoelectric pressuresensor that includes a membrane that protrudes directly into thepressure chamber through a bore in the pressure chamber. An edge of themembrane is welded to a housing of the piezoelectric pressure sensor.The pressure profile captured by the membrane acts onto a piezoelectricsensor that is arranged within the housing and near the membrane. Thepressure profile generates electric polarization charges on thepiezoelectric sensor, and these charges are transmitted electrically assignals via an electrode. The signals are proportional to the magnitudesof the pressures that constitute the pressure profile. The electrode isarranged on the piezoelectric sensor. By means of an electricalconductor, the signals are transmitted electrically from the electrodeto a socket for a plug connection of a signal cable that leads to anevaluation unit. The socket is arranged on a side of the housing thatfaces away from the membrane.

Additionally, U.S. Pat. No. 4,675,643, which is hereby incorporatedherein by this reference for all purposes, discloses a piezoresistivepressure sensor in which a sensor with piezoresistors applied thereongenerates signals under the action of a pressure profile detected by amembrane. Electrodes are electrically connected to the terminals of thepiezoresistors and transmit the signals into an evaluation unit viafeedthroughs in the form of slide bushings from a housing of the sensorand via contact surfaces to strands of electrical conductors.

In fact, during continuous use the pressure sensor is exposed to strongengine vibrations and high temperatures of 200° C. and above. These maylead to micro friction and fretting corrosion at the contact surfaces ofelectrodes, terminals, plug connections and feedthroughs, therebyleading to weakening of the mechanical stability of the signaltransmission. In addition, outgassing of the signal cable sheath mayoccur at high temperatures, and such gases cross-link locally byfriction polymerization and form deposits on the contact surfaces ofelectrodes, terminals, plug connections and feedthroughs. Furthermore,diffusion of base metals and local build-up of oxide layers on contactsurfaces of electrodes, terminals, plug connections and feedthroughs mayoccur at high temperatures. These effects may occur separately or incombination. As a result, the electrical resistance during signaltransmission may change. Thus, the electrical contact resistance mayincrease from the mΩ range by several orders of magnitude into the MΩrange and distort the signals transmitted to the evaluation unit,thereby resulting in incorrect signal evaluations. Generally, ensuringan electrical insulation of the signal transmission at high temperaturesis very important because electrical leakage currents may occur atcomponents of the pressure sensor, and such electrical leakage currentsmay distort the signal transmission. Furthermore, different expansioncoefficients of the components of the pressure sensor may lead to localmechanical stresses at high temperatures. Finally, the components of thepressure sensor may age prematurely at high temperatures. Such thermallyinduced mechanical stresses and such premature aging have detrimentaleffects on the service life of the pressure sensor.

A first object of the present invention is to provide a pressure sensorwherein signal distortion in signal transmission is effectivelyprevented. Another object of the present invention is to provide apressure sensor wherein the signal output and the evaluation unit aremechanically stable, even with strong permanent engine vibrations. It isan additional object of the present invention to provide a pressuresensor in which the components thereof are largely devoid of mechanicalstresses and premature aging even at high temperatures. Finally, itwould be desirable to be able to provide a process for thecost-effective manufacture of a pressure sensor having these attributes.

SUMMARY OF THE INVENTION

The invention relates to a pressure sensor that includes a sensorassembly and an evaluation unit. The sensor assembly includes a sensorand an electrode arrangement. The sensor responds to a pressure profileby generating electrical signals. The electrode arrangement transmitsthe signals to the evaluation unit, which includes an evaluation unithousing, an electric circuit board and a reinforcement element that ismechanically connected to the electric circuit board. Furthermore, thereinforcement element is arranged in a radial plane between the electriccircuit board and the evaluation unit housing and dampens mechanicalresonance vibrations of the electric circuit board that occur in theradial plane.

The inventors have perceived that while the electric circuit boardexhibits a greater expansion along a longitudinal axis of the pressuresensor, engine vibrations occurring during use of the pressure sensorgenerate mechanical resonance vibrations in a radial plane perpendicularto the longitudinal axis. In accordance with one aspect of the presentinvention, a reinforcement element is provided to reinforce the electriccircuit board in this radial plane. Preferably, the reinforcementelement fixes the electric circuit board relative to the evaluation unithousing so as to restrain the electric circuit board's freedom ofmovement in the radial plane. Thus, engine vibrations are only able toinduce in the electric circuit board, dampened mechanical resonancevibrations in the radial plane. Accordingly, the mechanical stress ofthe components involved in signal transmission of the piezoelectricpressure sensor in the area of the electric circuit board is permanentlyreduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be explained in more detail by wayof examples referring to the Figures in which:

FIG. 1 shows a cross-sectional view through a first embodiment of apiezoelectric pressure sensor with sensor assembly and evaluation unit;

FIG. 2 shows a cross-sectional view through a second embodiment of apiezoelectric pressure sensor with sensor assembly and evaluation unit;

FIG. 3 shows an enlarged cross-sectional view through a portion of apresently preferred embodiment of the sensor assembly according to FIG.1 or 2;

FIG. 4 shows a top view of a portion of the first embodiment of thepiezoelectric pressure sensor according to FIG. 1 without evaluationunit housing and without electrical insulation element;

FIG. 5 shows a side view of an electric circuit board of the firstembodiment of the piezoelectric pressure sensor according to FIG. 1 or4;

FIG. 6 shows a top view of the electric circuit board of the firstembodiment of the piezoelectric pressure sensor according to FIG. 1, 4,or 5;

FIG. 7 shows a top view of a portion of the second embodiment of thepiezoelectric pressure sensor according to FIG. 2 without evaluationunit housing and without electrical insulation element;

FIG. 8 shows a top view of the electric circuit board of the secondembodiment of the piezoelectric pressure sensor according to FIG. 2 or7;

FIG. 9 shows a side view of the electric circuit board of the secondembodiment of the piezoelectric pressure sensor according to FIG. 2, 7or 8;

FIG. 10 shows an enlarged top view of an area A of the first embodimentof the piezoelectric pressure sensor according to FIG. 4;

FIG. 11 shows an enlarged top view of an area B of the second embodimentof the piezoelectric pressure sensor according to FIG. 7;

FIG. 12 shows a view of a portion of the first embodiment of thepiezoelectric pressure sensor according to FIG. 4 during fitting of theelectrical insulation element on top;

FIG. 13 shows a view of a portion of the first embodiment of thepiezoelectric pressure sensor according to FIG. 4 or 12 after fitting ofthe electrical insulation element;

FIG. 14 shows in a cross-sectional view looking down the longitudinalaxis C-C′, the electrical insulation element according to FIG. 12 or 13;

FIG. 15 shows a top view of the first embodiment of the piezoelectricpressure sensor according to FIG. 1, 4, 12 or 13 prior to making thematerial bond between the electrode arrangement of the sensor assemblyand the electric circuit board of the evaluation unit;

FIG. 16 shows a top view of the first embodiment of the piezoelectricpressure sensor according to FIG. 1, 4, 12, 13 or 15 after the materialbond of the electrode arrangement of the sensor assembly to the electriccircuit board of the evaluation unit has been made; and

FIG. 17 shows an enlarged top view of an area of the first embodiment ofthe piezoelectric pressure sensor according to FIG. 15.

DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

FIGS. 1 and 2 show sections through two embodiments of the piezoelectricpressure sensor 1 according to the invention. The sections are shownalong a longitudinal axis CC′ of the mounted ready-to-use piezoelectricpressure sensor 1. The longitudinal axis CC′, a vertical axis AA′ (FIG.14) and a horizontal axis BB′ (FIG. 14) are perpendicular to each other.A direction along the longitudinal axis CC′ is called also alongitudinal direction, a direction perpendicular to the longitudinaldirection is also called a radial direction. As shown in FIG. 14, thevertical axis AA′ and the horizontal axis BB′ span a radial plane AB.Radial directions lie within the radial plane AB. In cross section, thepiezoelectric pressure sensor 1 and its components are generallycircular with the center point lying on the longitudinal axis CC′. Theadverb “generally” includes a variation from the circular form of ±10%.Knowing the present invention, the piezoelectric pressure sensor and itscomponents also may be rectangular, polygonal, etc. in cross section.Thus, an electric circuit board 51 is rectangular, for example.

The components of the piezoelectric pressure sensor 1 may bemechanically contacted with each other or may be mechanically connectedto each other. In the sense of the invention, a mechanical contact meansthat several components are merely placed in direct contact with eachother, while in the case of a mechanical connection several componentsare fixed to each other by means of material bonding, force closure orform closure. Thus, a mechanical contact is not the same as a mechanicalconnection. A mechanical contact is not pressure-tight. The adjective“pressure-tight” refers to resistance against pressure profiles of 10bar and more.

By material bonding is meant connection effected by soldering or weldingfor example. By form closure is meant positive fit joints such as bybolted joints or snap joints that are intended to be reversible withoutdamaging either of the joined elements. By force closure is meant aforce fit joint between two elements in contact with each other thatrequires the application of force to at least one of the elements by atool in order to effect the connection such as screwed joints or rivetedjoints or press-fit joints, and while these are in some sensereversible, there might be damage done by the actions required forseparation of the two elements. Another type of force closure would bejoints held together by magnetic force attraction, yet these could beseparated without damaging either of the joined elements.

As shown in FIGS. 1 and 2, an embodiment of a piezoelectric pressuresensor 1 in accordance with the present invention includes a sensorassembly 2 and an evaluation unit 5. As shown in FIGS. 1 and 2, theevaluation unit 5 is electrically and mechanically connected directly tothe sensor assembly 2. FIG. 3 shows the sensor assembly 2 as asemi-finished product. The evaluation unit 5 also is a semi-finishedproduct having multiple components, as represented in FIGS. 4 to 9 and12 to 14. FIGS. 10, 11 and 17 show enlarged top views of areas A (takenfrom FIG. 4), B (taken from FIG. 7) and C (taken from FIG. 15) of theelectrical and mechanical connection of the sensor assembly 2 to theevaluation unit 5. Furthermore, FIGS. 15 and 16 show views of theprocess of manufacturing the electrical and mechanical connection of thesensor assembly 2 to the evaluation unit 5.

As shown in FIGS. 1 and 2 for example, the sensor assembly 2 is arrangedin a front area of the piezoelectric pressure sensor 1. As shown in FIG.3 for example, the sensor assembly 2 includes a membrane 21 and a sensorhousing assembly 20 that can include a sealing cone 20.1 and a sensorflange 20.2. As shown in FIG. 3 for example, some embodiments of thesensor housing assembly 20 can include an anti-strain sleeve, whichdesirably can be formed having a circumferentially continuous flangeextending radially from the front thereof and that extends into acomplementarily shaped recess that is defined between the front edge ofthe sensor flange 20.2 and a rearwardly facing front ledge of thesealing cone 20.1. In such embodiments, the anti-strain sleeve ispermanently connected as by welding to the radially inwardly facingsurface of a front portion of the sensor flange 20.2 and welded to thefront edge of the sensor flange 20.2. Additionally, the front edge ofthe anti-strain sleeve is permanently connected, as by material bondingsuch as welding for example, to the rearwardly facing surface of thecircumferentially outer portion of the membrane 2. In an alternativeembodiment, the forward end of the sensor flange 20.2 is configured in away that emulates the presence of the anti-strain sleeve, which thusneed not be provided as a separate component. In a further alternativeembodiment, the sensor housing assembly 20 can be provided as a unitarycomponent instead of two or more multiple components (e.g., 20.1, 20.2and/or anti-strain sleeve) that are permanently mechanically connectedtogether to become integrated as a single component.

As shown in FIG. 3 for example, the sensor assembly 2 also includes apiezoelectric sensor 22 and an electrode arrangement 23. Thepiezoelectric pressure sensor 1 is mechanically connected to a wall of apressure chamber, and the membrane 21 protrudes directly into thepressure chamber through a bore that is defined through the wall. Themechanical connection between the wall and the piezoelectric pressuresensor 1 desirably is made by a force closure or by a form closure.During use of the piezoelectric pressure sensor 1, the front area of thepiezoelectric pressure sensor 1 is permanently exposed to strong enginevibrations and high temperatures in the vicinity of the pressurechamber. The terms “front” and “rear” are used for the piezoelectricpressure sensor 1 and its components to indicate by “front” an area thatis oriented towards the membrane 21, while “rear” refers to an area thatfaces away from the membrane 21.

As shown in FIG. 3 for example, the sensor flange 20.2, which is alsoreferred to as the reinforcement casing 20.2, accommodates thepiezoelectric sensor 22 and components of the piezoelectric pressuresensor 1 adjacent to the piezoelectric sensor 22. Sealing cone 20.1 andsensor flange 20.2 desirably consist of mechanically flexible materialsuch as pure metals, nickel alloys, cobalt alloys, iron alloys, etc. andare mechanically connected to each other. The mechanical connectionbetween the sealing cone 20.1 and the sensor flange 20.2 desirably isachieved by means of material bonding such as welding, diffusionwelding, thermo compression bonding, soldering, etc. By being composedof these materials and connected in this way, the sealing cone 20.1 andthe sensor flange 20.2 can absorb mechanical tensions originating fromthe mechanical connection of the piezoelectric pressure sensor 1 to thewall of the pressure chamber. If such mechanical tensions weretransmitted via the sensor housing assembly 20 onto the piezoelectricsensor 22, they would disturb the detection of the pressure profile aswell as distort the signals generated by the piezoelectric sensor 22.Accordingly, the sensor housing assembly 20 also shields thepiezoelectric sensor 22 by preventing the transfer of mechanicaltensions originating from the mechanical connection of the piezoelectricpressure sensor 1 to the wall of the pressure chamber. Knowing thepresent invention, and as mentioned above, the skilled person also canmanufacture the sensor housing assembly 20 without a sensor flange 20.2defining a separate component from the sealing cone 20.1 so that thesensor housing assembly 20 consists only of a sealing cone 20.1 as aunitary structure that emulates the configuration of the combinedsealing cone 20.1, sensor flange 20.2 and/or anti-strain sleeve shown inFIG. 3.

The frontal membrane 21 consists of mechanically flexible material suchas pure metals, nickel alloys, cobalt alloys, iron alloys, etc. As shownin FIG. 3 for example, a circumferentially outwardly disposed edge ofthe membrane 21 is mechanically connected around its entire perimeter tothe reinforcement casing 20.2. An annular shaped area of the centrallydisposed and rearwardly-facing end of the membrane desirably can bemechanically connected to the entire perimeter of the front end of apre-stressing sleeve, which desirably is formed as a hollowcylindrically shaped component. The rear end of the pre-stressing sleevedesirably can be mechanically connected to the front end of apre-stressing body, which desirably is formed as a hollow cylindricallyshaped component. These mechanical connections desirably are carried outby means of material bonding such as welding, diffusion welding, thermocompression bonding, soldering, etc. A pressure captured by the membrane21 acts as a normal force onto the piezoelectric sensor 22. Details ofthe pre-stressing sleeve and pre-stressing body are disclosed in U.S.patent application serial no. 15-215,712, filed Jul. 21, 2016, which ishereby incorporated herein by this reference for all purposes.

As shown in FIG. 3 for example, the piezoelectric sensor 22 ispositioned in direct alignment behind the membrane 21 on thelongitudinal axis CC′ and includes a first support element 22.1, asecond support element 22.3 as well as a piezoelectric sensor element22.2. Relative to the longitudinal axis CC′, the piezoelectric sensorelement 22.2 is arranged between the first and second support elements22.1 and 22.3, and this arrangement evenly distributes the normal forceonto the piezoelectric sensor element 22.2. The support elements 22.1,22.3 desirably are in the form of cylinders or hollow cylinders anddesirably consist of electrically conductive and mechanically rigidmaterial such as pure metals, nickel alloys, cobalt alloys, iron alloys,electrically conductive ceramics, ceramics having an electricallyconductive coating, etc. The surface of the membrane 21 is in mechanicalcontact with the first support element 22.1. Furthermore, the firstsupport element 22.1 and the second support element 22.3 alsomechanically contact the piezoelectric sensor element 22.2 via theirsurfaces. These surface mechanical contacts also desirably may be madethrough mechanical connections, which desirably are made by materialbonding such as diffusion welding, thermo compression bonding,soldering, etc. Knowing the present invention, those skilled in the artalternatively can implement the piezoelectric sensor 22 without supportelements (22.1 and 22.3) or can implement a piezoelectric sensor 22 withonly one support element (22.1) arranged between the membrane 21 and thepiezoelectric sensor element 22.2.

The piezoelectric sensor element 22.2 desirably is cylindrical orhollow-cylindrical in shape and consists of piezoelectric material suchas quartz (SiO₂ monocrystal), calcium gallo-germanate (Ca₃Ga₂Ge₄O₁₄ orCGG), langasite (La₃Ga₅SiO₁₄ or LGS), tourmaline, galliumorthophosphate, etc. The piezoelectric sensor element 22.2 is orientedto have a high sensitivity for the pressure profile to be captured.Advantageously, the piezoelectric sensor element 22.2 is oriented insuch a way that the normal force affecting the membrane 21 acts on thesame surfaces of the piezoelectric sensor element 22.2 that experiencethe changes in negative and positive electric polarization attributableto pressures affecting the membrane 21. The normal force can act ontothe surface of the piezoelectric sensor element 22.2 in a loading orrelieving manner. Under a mechanical load due to the normal force,negative polarization charges are generated and migrate onto one of theopposite surfaces of the piezoelectric sensor element 22.2. If thenormal force has a relieving impact, negative polarization charges aredrawn away from one of the opposite surfaces of the piezoelectric sensorelement 22.2 and this directional migration of negative charge producesan electrical effect as if positive polarization charges are produced.Knowing the present invention, the skilled artisan can of course usemore than one piezoelectric sensor element 22.2.

As shown in FIG. 3 for example, the electrode arrangement 23 ispositioned along the longitudinal axis CC′ on the side of thepiezoelectric sensor 22 that faces away from the membrane 21 directlybehind the piezoelectric sensor 22. The electrode arrangement 23desirably has a cylindrically shaped charge pick-off 23.1 at the frontopposite end thereof and a rod-shaped charge output 23.2 at the oppositeback end thereof. The charge pick-off 23.1 desirably can take the formof a circular disk having a much larger diameter (and surface area) thanthe diameter of the charge output 23.2, which desirably elongates alongthe longitudinal axis CC′ from the rear surface of the charge pick-off23.1. The charge pick-off 23.1 and the charge output 23.2 areelectrically connected to each other. The electrode arrangement 23desirably consists of an electrically conductive material such as puremetals, nickel alloys, cobalt alloys, iron alloys, etc. The chargepick-off 23.1 and the charge output 23.2 desirably may be formedintegrally by mechanically connecting the charge pick-off 23.1 to thecharge output 23.2 in a permanent way, which desirably can be effectedby material bonding. However, any type of mechanical connection may beused such as, for example, form closure and force closure.Alternatively, the charge pick-off 23.1 and the charge output 23.2desirably may be formed as a unitary structure such as would be the caseif a single metal stock was milled on a lathe to form the chargepick-off 23.1 at one end of the stock and the charge output 23.2 at theother end of the stock. A similar unitary element forming the chargepick-off 23.1 and the charge output 23.2 also could be obtained in asingle molding operation. The material of the electrode arrangement 23preferably has a coefficient of linear thermal expansion in the range of10 to 18 ppm/° C., preferably in the range of 10 to 12 ppm/° C.

As shown in FIG. 3 for example, the entire front surface of the chargepick-off 23.1 desirably is in electrical contact with a rear surface ofthe second support element 22.3 where charges are discharged. In sodoing, all areas where high local electric voltages and electricalleakage currents may occur under the impact of a normal force are sureto be covered by such contact. The surface electric contact of thecharge pick-off 23.1 and the second support element 22.3 is achieved bybringing the surfaces thereof in mechanical contact with each other.Knowing the present invention, the skilled artisan also can achieve thesurface mechanical contact by a mechanical connection, which desirablycan be achieved by means of material bonding such as diffusion welding,thermo compression bonding, soldering, etc.

Electric polarization charges with a first polarity are received assignals by the electrode arrangement 23 and are transmitted to theevaluation unit 5. Electric polarization charges with a second polarityare received via the membrane 21 or a clamping sleeve from the groundedsensor flange 20.2 as signals from the return line and are fed to theevaluation unit 5. The electrical current of the signals or the signalsfrom the return line, respectively, is on the order of 1 pA and thusvery small. Electric signals this small are subject to being distortedby electrical leakage currents through the electrical insulationmaterial. Although not shown in the Figures, a skilled artisan knowingthe present invention also can implement the signal transmission bymeans of a shield (guard) made of electrically conductive material thatsurrounds the signal line and that is on a reference potential of thesignal line. In this case, electrical leakage currents flow between thereference potential and guard. No electrical leakage currents flowbetween guard and signal line because the electrical potentialdifference between them is zero. The shield may surround the signalline, signal conductors of the electric circuit board, electricalterminals of electronic components of the electric circuit board, etc.Furthermore, those skilled in the art also can use electric polarizationcharges with a second polarity as further signals. Thus, the skilledartisan can transmit the electric polarization charges with the secondpolarity from the ground potential in an electrically insulated mannerto the evaluation unit. This may be achieved by an electrical connectionby means of material bonding such as crimping, etc. of the sensorhousing assembly 20 to an electromagnetic shielding of the evaluationunit housing 50 (described more fully below).

As shown in FIG. 3 for example, the electrode arrangement 23 iselectrically insulated against the sensor flange 20.2 by an electricinsulation body 25, which desirably has the form of a hollow cylinderand desirably is made of electrically insulating and mechanically rigidmaterial such as ceramics, A1 ₂O₃ ceramics, sapphire, etc. On thelongitudinal axis CC′, the electric insulation body 25 is positioneddirectly behind the charge pick-off 23.1 on the side of the chargepick-off 23.1 that faces away from the membrane 21. The electricinsulation body 25 is in mechanical contact over its entire surface withthe charge pick-off 23.1. The charge output 23.2 extends up to an end ofthe sensor assembly 2 that faces away from the piezoelectric sensor 22.

A compensation element 26 desirably can be provided to compensate fordifferent thermal expansion coefficients of the components of thepiezoelectric pressure sensor 1. As shown in FIG. 3 for example, thecompensation element 26 desirably has the form of a hollow cylinder andis made of mechanically rigid material such as from pure metals, nickelalloys, cobalt alloys, iron alloys, ceramics, Al₂O₃ ceramics, sapphire,etc. On the longitudinal axis CC′, the compensation element 26 isdisposed directly behind the electric insulation body 25 on the side ofthe electric insulation body 25 facing away from the membrane 21. In theembodiment of the sensor assembly 2 according to FIG. 3, thecompensation element 26 mechanically contacts the electric insulationbody 25 over its entire surface. Knowing the present invention, thoseskilled in the art also can arrange the compensation element on the sideof the charge pick-off that faces the membrane 21 where it replaces thesupport element. The compensation element 26 may be arranged between themembrane 21 and the piezoelectric sensor element 22.2 instead of thefirst support element 22.1. However, the compensation element 26 alsomay be arranged between the piezoelectric sensor element 22.2 and thecharge pick-off 23.1 instead of the second support element 22.3.

As shown in FIGS. 1 and 2 for example, the evaluation unit 5 includes acircuit board housing 50 and an electric circuit board 51. The circuitboard housing 50 is also called the evaluation unit housing 50. As shownin FIGS. 12, 13, 14 and 17 for example, the evaluation unit 5 desirablyincludes a reinforcement element 52.1, 52.2. The electric circuit board51 and the reinforcement element 52.1, 52.2 are accommodated in theevaluation unit housing 50 of the evaluation unit 5. Referring to FIGS.1, 2, 12 and 13 for example, it can be appreciated that thereinforcement element 52.1, 52.2 is arranged in the radial directionbetween the electric circuit board 51 and the evaluation unit housing50. The reinforcement element 52.1, 52.2 is also referred to aselectrical insulation element 52.1, 52.2.

The electric circuit board 51 consists of a base material such aspolytetrafluoroethylene, polyimide, Al₂O₃ ceramics, laminates ofhydrocarbon-ceramics, etc. The base material is electrically insulatinghaving a specific volume resistance of that is superior to 10¹⁵ Ωcm atroom temperature but at least equal to 10¹⁵ Ωcm at room temperature,preferably superior to 10¹⁶ Ωcm at room temperature but at least equalto 10¹⁶ Ωcm at room temperature. The base material forming the electriccircuit board 51 desirably is adapted to permanent service temperaturesof less than or equal to 280° C. Specifically, the very high specificvolume resistance ensures that the signal output cannot be distorted byelectrical leakage currents even at permanent service temperatures justbelow 280°. Preferably, the base material has a thermal coefficient oflinear expansion in the range of 10 to 18 ppm/° C., preferably in therange of 10 to 12 ppm/° C. which generally is equal to the thermalcoefficient of linear expansion of the charge output 23.2 and/or theelectrical connecting element 53 (described more fully below).

The electric circuit board 51 desirably includes a high temperatureregion 51.1 and a normal temperature region 51.2. As shown in FIGS. 5,6, 8 and 9 for example, the high temperature region 51.1 is in a frontto central area of the electric circuit board 51. The high temperatureregion 51.1 faces the sensor assembly 2. The normal temperature region51.2 is in a central to rear area of the electric circuit board 51. Thenormal temperature region 51.2 faces away from the sensor assembly 2. Inthe high temperature region 51.1 of the electric circuit board, 51, thepermanent service temperature is less than or equal to 280° C. The hightemperature region 51.1 preferably extends over 80% of the length of theelectric circuit board 51, preferably over 50% of the length of theelectric circuit board 51, preferably over 30% of the length of theelectric circuit board 51, preferably over 20% of the length of theelectric circuit board 51.

The electric circuit board 51 includes electrical signal conductors thatare made from electrically conductive material such as from pure metals,nickel alloys, cobalt alloys, iron alloys, etc. A bottom surface of theelectrical signal conductors rests on the electric circuit board 51.Preferably, the electrical signal conductors are multi-layered, and afirst layer consists of a palladium nickel alloy while a second layer ismade from gold. The first layer of a palladium nickel alloy is directlyplated onto the base plate of the circuit board 51 while the secondlayer made from gold is vapor-deposited onto the first layer of apalladium nickel alloy. The first layer of a palladium nickel alloyserves as a barrier for diffusion of gold of the second layer into thebase material of the electric circuit board 51. The second layer of goldserves as protection against corrosion having a low electricalresistance and very good soldering properties. A top surface of theelectrical signal leads either is open (surface microstrip) or coveredwith solder mask (coated microstrip). Preferably, in order to preventheat conduction via the electrically conductive material of theelectrical signal conductors from the high temperature region 51.1 tothe low temperature region 51.2, no electric signal conductors arearranged in the high temperature region 51.1 of the electric circuitboard 51. Alternatively, in order to minimize heat conduction via theelectrically conductive material of the electrical signal conductorsfrom the high temperature region 51.1 to the low temperature region51.2, only electrical signal conductors for signal transmission arearranged in the high temperature region 51.1 of the electric circuitboard 51. With the exception of the electrical signal conductors forsignal transmission, no other electrical signal conductors are arrangedin the high temperature region 51.1 of the electric circuit board 51 inthis alternative embodiment.

On the electric circuit board 51 are mounted electronic components suchas electric resistors, electric capacitors, semiconductors, processors,etc. In order to avoid premature aging of the electronic components,they desirably are positioned only in the normal temperature region 51.2of the electric circuit board 51. In the normal temperature region 51.2,the permanent service temperature is no greater than 120° C. so that theelectronic components must only comply with an extended industrialstandard of an upper permanent service temperature of +125° C. and thusare relatively inexpensive and readily available. Those skilled in theart being aware of the present invention may of course also use arelatively expensive electric circuit board 51 such as one with a thicklayer with a base made of nickel alloys, cobalt alloys, iron alloys, A1₂O₃ ceramics, etc. with a permanent service temperature of more than500° C.

Solder mask desirably is applied to the electric circuit board 51 andprotects the electronic components and electrical signal conductors fromcorrosion. Solder mask also prevents wetting of the base material of theelectric circuit board 51 with soldering material during mounting of theelectric circuit board 51 with electronic components and in this mannerprevents the formation of accidental electrical connections duringmounting. Advantageously, no solder mask is applied in the hightemperature region 51.1 of the electric circuit board 51. However, thespecific volume resistance of solder mask at room temperature is muchsmaller than 10¹⁴ Ωcm so that at high temperatures just below 280° C.there is no longer achieved a sufficient resistance to leakage currentswhich can lead to signal distortion during signal transmission.Furthermore, solder mask is not permanently heat-resistant at hightemperatures just below 280° C. and may melt or burn and, thus, impairthe function of the evaluation unit.

Furthermore, as shown in FIGS. 1, 2, 4, 5, 6, 7, 8, 9, 10 and 11 forexample, the evaluation unit 5 desirably includes an electricalconnection element 53, a signal cable flange 54 and a signal cable 55.The electrical connecting element 53 is electrically connected toelectronic components via at least one electrical signal conductor. Theelectrical connection desirably is made by means of material bondingsuch as soldering, crimping etc. Signals received from the electrodearrangement 23 are fed via the charge output 23.2 to the electricalconnection element 53 of the evaluation unit 5 and are fed from theelectrical connection element 53 of the evaluation unit 5 via theelectrical signal conductor to the electric circuit board 51. The signaltransmission from the electrode arrangement 23 to the evaluation unit 5occurs through material bonding only. Preferably, the signal transferoccurs from an electrical contact of the surface of the sensor 22 withthe electrode arrangement 23 to the evaluation unit 5 only throughmaterial bonding. Within the evaluation unit 5, signals may beelectrically amplified as well as subjected to initial evaluation.Preferably, both signals from the charge output 23.2 and signals fromthe return line are amplified and evaluated in the evaluation unit 5.The signals from the charge output 23.2 and signals from the return lineare proportional to the amount of the pressure profile captured by themembrane 21. The signal cable 55 is configured and connected so as totransmit both amplified signals from the charge output 23.2 and returnline signals on the one hand and on the other hand both signals from thecharge output 23.2 and return line signals that already have beenevaluated. Front ends of the signal cables 55 are electrically andmechanically connected to the normal temperature region 51.2 of theelectric circuit board 51. This electrical and mechanical connectiondesirably is achieved by means of material bonding such as soldering,crimping, etc. Knowing the present invention, the skilled artisan alsocan mechanically and electrically connect the charge output 23.2directly to a signal conductor of the electric circuit board 51 so thatno electrical connection element 53 is required for signal transmission.This electrical and mechanical connection is also desirably made bymaterial bonding such as soldering, crimping, etc.

As shown in FIGS. 4, 10 and 11 for example, the electrical connectingelement 53 desirably has the form of a hollow cylinder and consists ofelectrically conductive material such as pure metals, nickel alloys,cobalt alloys, iron alloys, etc. The material of the electricalconnection element 53 preferably has a thermal coefficient of linearexpansion in the range of 10 to 18 ppm/° C., preferably in the range of10 to 12 ppm/° C. Thus, the magnitude of the thermal coefficient oflinear expansion of the electrical connection element 53 is comparableto the magnitude of the thermal coefficient of linear expansion of thesensor assembly 2 and/or the electric circuit board 51.

In a first embodiment of a piezoelectric pressure sensor 1 according toFIGS. 1, 4 to 6, 10, 12, 13 and 15 to 17, the electrical connectionelement 53 desirably includes an adapter 53.0 in the form of a socket.Preferably, the adapter 53.0 is in the form of a socket with a slit. Theadapter 53.0 in the form of a socket desirably is arranged in the hightemperature region 51.1 of the electric circuit board 51. For signaltransmission, the adapter 53.0 in the form of a socket desirably isconnected to an electrical signal conductor of the electric circuitboard 51 by material bonding, which desirably is achieved by welding,diffusion welding, thermo compression bonding, soldering, etc.Furthermore, the adapter 53.0 in the form of a socket desirably ismechanically connected to the electric circuit board 51. This mechanicalconnection serves a dual function, both for attachment of the adapter53.0 on electric circuit board 51 and for signal transmission.Preferably, the mechanical connection is achieved by material bondingsuch as welding, diffusion welding, thermo compression bonding,soldering, etc. Knowing the present invention, the skilled artisan isalso able to implement this dual function mechanical connection throughform closure or force closure.

In a second embodiment of a piezoelectric pressure sensor 1 according toFIGS. 2, 7 to 9 and 11, the electrical connection element 53 desirablyincludes an annular adapter 53.1 and a compensation element 53.2. Theannular adapter 53.1 and the compensation element 53.2 are preferablyintegrally formed, either as a unitary structure or permanently joinedtogether to function as one. The electrical connection element 53extends along the longitudinal axis CC′. The annular adapter 53.1 ispositioned at a front end of the electrical connection element 53. Thecompensation element 53.2 mechanically supports the annular adapter53.1. As shown in FIG. 11 for example, the compensation element 53.2desirably includes at least one bend such as a Z bend, an U bend, anexpansion loop, etc. The bend compensates for differences in the thermalcoefficients of linear expansion of signal-transmitting components ofthe piezoelectric pressure sensor 1. The bend also compensates formanufacturing tolerances along the longitudinal axis CC′ of componentsof the sensor assembly 2 and the evaluation unit 5. In the area of thebend, the compensation element 53.2 can expand or contract and thusreduce the occurrence of thermally induced mechanical tensions and/or ofmanufacturing tolerances to uncritical values. The compensation element53.2 extends over the high temperature area 51.1 of the electric circuitboard 51. Knowing the present invention, those skilled in the art arealso able to combine these two embodiments of a piezoelectric pressuresensor 1. Thus, the adapter in the form of a socket of the firstembodiment may be combined at the front end of the compensation elementof the second embodiment.

Generally, the compensation element 53.2 extends over the entire hightemperature region 51.1 of the electric circuit board 51. For signaltransmission, the compensation element 53.2 is connected by means ofmaterial bonding to a signal conductor of the electric circuit board 51in the low temperature range 51.2 of the electric circuit board 51. Thismaterial bond desirably is made by welding, diffusion welding, thermocompression bonding, soldering, etc. In addition, the compensationelement 53.2 is mechanically connected to the electric circuit board 51.For attachment of the compensation element 53.2 on the electric circuitboard, 51, the mechanical connection is preferably made by means of formclosure and force closure by inserting at least one leg of thecompensation element 53.2 into at least one corresponding opening in thehigh temperature region 51.1 of the electric circuit board 51. The legdesirably is deformable, whether elastically or plastically, and iscompressed when the leg is inserted in the opening in the hightemperature region 51.1 of the electric circuit board 51. Suchcompression results in mechanical pre-stressing, which retains the legin place by means of form closure and force closure. One particularlydesirable embodiment of the leg can be provided in the form of a springsuch as a flat spiral spring with two spring hinges that are connectedto each other at their front and rear ends and are spaced apart in acentral region thereof. When the two spring hinges are inserted into theopening, the two spring hinges are elastically deformed in their centralregions. Alternatively, the mechanical connection for the attachment ofthe compensation element 53.2 in the high temperature region 51.1 of theelectric circuit board 51 also may be achieved by means of materialbonding, which desirably is made by welding, diffusion welding, thermocompression bonding, soldering, etc.

As shown in FIGS. 10 and 11 for example, the charge output 23.2 isjoined with the electrical connection element 53. The rear end of chargeoutput 23.2 protrudes along the longitudinal axis CC′ into the adapter53.0 in the form of a socket or the annular adapter 53.1. In this area,an outer surface of the charge output 23.2 relative to longitudinal axisCC′ and an inner surface of the adapter 53.0 in the form of a socket orthe annular adapter 53.1 relative to longitudinal axis CC′ areelectrically and mechanically connected to each other. This electricaland mechanical bond desirably is made by material bonding such aswelding, diffusion welding, thermo compression bonding, soldering,crimping, etc. Thus, the charge output 23.2 forms a material bond to theelectrical connection element 53 in certain areas. This material bondingin certain areas desirably can be achieved by spot welding or by seamwelding around the entire perimeter. The material bond prevents theoccurrence of micro friction, fretting corrosion, frictionpolymerization or the build-up of a layer of oxide on contact surfacesof electrodes, terminals, connectors and feedthroughs during use of thepiezoelectric pressure sensor 1 and effectively prevents signaldistortions. Knowing the present invention, those skilled in the art ofcourse also can use a differently shaped electrical connector 53. Thus,the electrical connection element 53 can have the form of a plate or ofa half shell. In such alternative embodiments, the charge output 23.2does not extend into the electrical connecting element 53. For makingthe electrical and mechanical connection in such alternativeembodiments, the charge output 23.2 is placed onto the electricalconnecting element 43 having the form of a plate or a half shell.

The reinforcement element 52.1, 52.2 has the form of a hollow cylinderthat elongates along the longitudinal axis CC′ and consists ofelectrically insulating material that is dimensionally stable up totemperatures of at least 120° C., preferably of at least 150° C., suchas polyether ether ketone (PEEK), polytetrafluoroethylene, polyimide,hexafluoropropylene vinylidene fluoride copolymer (FKM), etc. Thematerial of the reinforcement element 52.1, 52.2 preferably has athermal coefficient of linear expansion in the range of 10 to 50 ppm/°C. As shown in FIG. 14 for example, the reinforcement element 52.1, 52.2is arranged around the electric circuit board 51, and the transversecross-section of the reinforcement element 52.1, 52.2 lies in the radialplane AB. The reinforcement element 52.1, 52.2 surrounds the electriccircuit board 51 in certain areas. The reinforcement element 52.1, 52.2is arranged between the electric circuit board 51 and the evaluationunit housing 50 with respect to the radial plane AB. Preferably, thereinforcement element 52.1, 52.2 encloses the electric circuit board 51in certain areas along the longitudinal axis CC′. Preferably, thereinforcement element 52.1, 52.2 fully encloses the electric circuitboard 51, which in the representation according to FIG. 14 is alsointended to include enclosing by 360° in the radial plane AB. In thelongitudinal direction along the longitudinal axis CC′, the electriccircuit board 51 desirably may penetrate the reinforcement element 52.1,52.2 in certain areas. For this purpose, the reinforcement element 52.1,52.2 may have at least one opening through which the electric circuitboard 51 also may be visible and accessible from a vantage point that isradially outside the reinforcement element 52.1, 52.2 in certain areasof the reinforcement element 52.1, 52.2.

Preferably, as shown in FIG. 14 for example, the reinforcement element52.1, 52.2 includes several parts and consists of at least two shells52.1, 52.2. Preferably, the shells 52.1, 52.2 are identical. Preferably,the shells 52.1, 52.2 are interchangeable parts, thereby loweringproduction costs. The shells 52.1, 52.2 may be mechanically connected tothe electric circuit board 51 and/or mechanically connected to eachother. This mechanical connection can be made via form closure and/ormaterial bonding and/or force closure. This mechanical connection may bereversibly without damaging the individual parts, or once connectedtogether the parts are irreversibly detachable without being damaged.Preferably, the two shells 52.1, 52.2 may be mechanically connected tothe electric circuit board 51 or to each other via at least oneprotruding locking element 52.3, 52.3′. Preferably, the locking element52.3, 52.3′ of one of the shells 52.1, 52.2 engages a correspondingopening of the other shell 52.1, 52.2. Preferably, one locking element52.3, 52.3′ of one of the shells 52.1, 52.2 engages the electric circuitboard 51 through a corresponding opening of the other shell 52.1, 52.2.

Preferably, the shells 52.1 52.2 are not mirror-symmetrical with respectto the vertical axis AA′. In the transverse cross sectional view of theshell 52.1, 52.2 according to FIG. 14, the two protruding lockingelements 52.3, 52.3′ of the shell 52.1, 52.2 are arranged to the leftand the right of the vertical axis AA′. Along the longitudinal axis CC′,the two locking elements 52.3, 52.3′ are not arranged in the same radialplane AB; therefore, the locking element 52.3 on the right isrepresented by a dashed line. Thus, the electric circuit board 51 isarranged between the two shells 52.1, 52.2. As shown in FIG. 17 forexample, the reinforcement element 52.1, 52.2 defines at least onewindow 52.4 in the connection area between the charge output 23.2 andthe electrical connecting element 53. Through the window 52.4, thecharge output 23.2 and the electrical connection element 53 areaccessible from the outside and may be approached by means of a joiningtool.

Alternatively, the reinforcement element 52.1, 52.2 is made from onecontinuous piece without a window. Such an embodiment of thereinforcement element 52.1, 52.2 made from one piece without a window ispushed over the electric circuit board 51 in the longitudinal directionor is bent over the electric circuit board 51 in the radial direction bymeans of a flexure bearing.

During use of the piezoelectric pressure sensor 1, mechanical vibrationsmay be induced in the electric circuit board 51 due to enginevibrations. The electric circuit board 51 is a system capable ofoscillating. The engine vibrations exhibit a broad band of frequencies.Resonance frequencies are those frequencies of the engine vibrationswhere an amplitude of the oscillating system is greater than thatinduced by adjacent frequencies of the engine vibrations. Resonanceoscillations are oscillations of the electric circuit board 51 withresonance frequencies. However, in accordance with one aspect of thepresent invention, the reinforcement element 52.1, 52.2 mechanicallyreinforces the electric circuit board 51 against mechanical resonancevibrations in the radial plane AB and/or along the longitudinal axisCC′. Preferably, the reinforcing element 52.1, 52.2 fixes the electriccircuit board 51 in its freedom of movement in the radial plane ABrelative to the evaluation unit housing 50. To fix in this sense meansto hold the electric circuit board 51 immobile relative to theevaluation unit housing 50. Preferably, the electric circuit board 51,which is arranged between the shells 52.1, 52.2 and is mechanicallyconnected to the shells, 52.1, 52.2, forms a rigid body againstmechanical resonance vibrations in the radial plane AB and/or along thelongitudinal axis CC′. The reinforcement element 52.1, 52.2 makes alinear or surface mechanical contact with the electric circuit board 51.Engine vibrations occurring during use of the piezoelectric pressuresensor 1 are only able to induce dampened mechanical resonancevibrations in the radial plane AB or along the longitudinal axis CC′ inthe electric circuit board 51 that is reinforced in this manner, wherebythe mechanical stress of the components involved in signal transmissionof the piezoelectric pressure sensor 1 in the area of the electriccircuit board 51 is permanently reduced.

An additional reinforcement of the electric circuit board 51 againstbending loads along the longitudinal direction and/or along the radialdirection desirably is achieved by an interference fit from theevaluation unit housing 50 to the reinforcement element 52.1, 52.2. Inthis case, the evaluation unit housing 50 presses the reinforcementelement 52.1, 52.2 onto the electric circuit board 51 in certain areas.In addition, the charge output 23.2 and the electrical connectionelement 53 are positioned in the window 52.4 in a mechanically rigidmanner by the interference fit. The evaluation unit housing 50 isslidable along the longitudinal axis CC′ to be moved over thereinforcement element 52.1, 52.2. The reinforcement element 52.1, 52.2desirably includes several individual sections 52.6, 52.6′, 52.6″ thatare successively spaced end-to-end along the longitudinal axis CC′. Inthe embodiment according to FIGS. 12 and 13 for example, thereinforcement element 52.1, 52.2 includes three such individual sections52.6, 52.6′, 52.6″. Preferably, each section 52.6, 52.6′, 52.6″ has alength of 30 mm, preferably a length of 60 mm, preferably a length of 90mm measured along the longitudinal axis CC′. The evaluation unit housing50 is slidable along the longitudinal axis CC′ from a rear section 52.6″to a central section 52.6′ and from the central section 52.6′ to a frontsection 52.6 over the reinforcement element 52.1, 52.2. Preferably, thereinforcement element 52.1, 52.2 has different outer diameters in therear section 52.6″, in the central section 52.6′ and in the frontsection 52.6. Preferably, each of the sections 52.6, 52.6′, 52.6″extends over 33% of the length of the electric circuit board 51. Thus,in the longitudinal direction, the outer diameter of the reinforcementelement 52.1, 52.2 is stepped successively from section to section. Anouter diameter of the rear section 52.6″ of the reinforcement element52.1, 52.2 is smaller than/equal to the inner diameter of the evaluationunit housing 50. The evaluation unit housing 50 is manually slidablesmoothly over the reinforcement element 52.1, 52.2. An outer diameter ofthe central section 52.6′ of the reinforcement element 52.1, 52.2 isslightly oversized as compared to the inner diameter of the evaluationunit housing 50. If such an oversize exists, the evaluation unit housing50 is manually slidable smoothly over the reinforcement element 52.1,52.2. An outer diameter of the front section 52.6 of the reinforcementelement 52.1, 52.2 has a larger oversize as compared to the innerdiameter of the evaluation unit housing 50. In the case of a largeroversize, the evaluation unit housing 50 is no longer manually slidableover the reinforcement element 52.1, 52.2. The oversizes are chosendepending on the material so that the mechanical stresses that permitthe interference fit are not exceeded. Knowing the present invention,the skilled artisan is also able to implement the reinforcement elementwithout a central section and thus having only a front section and arear section. Furthermore, the skilled artisan can implement areinforcement element without a stepped outer diameter in which theouter diameter generally increases steadily from the rear to the frontregion.

As shown in FIGS. 12 and 13 for example, the reinforcement element 52.1,52.2 electrically insulates the electric circuit board 51 from theevaluation unit housing 50 (FIGS. 1 and 2 for example). As shown in FIG.14 for example, the reinforcement element 52.1, 52.2 includes at leastone bending zone 52.5 to compensate for differences in the thermalcoefficient of linear expansion between the electric circuit board 51,the reinforcement element 52.1, 52.2 and/or the evaluation unit housing50. The bending zone 52.5 is formed as a groove that extends inwardly inthe radial direction and axially in the longitudinal direction. In thearea of the bending zone 52.5, the reinforcement element 52.1, 52.2 mayexpand or contract elastically and in this manner reduce thermallyinduced mechanical stresses to uncritical values, and in particular aplastic deformation of the reinforcement element 52.1 52.2 that isdetrimental for its function may be avoided. Knowing the presentinvention, the skilled artisan also can implement the bending zone 52.5in the form of at least one recess in the material of the reinforcementelement 52.1, 52.2 or as a flexure hinge, etc. The reinforcement element52.1, 52.2 dampens the spreading of engine vibrations from the sensorflange 20.2 and the evaluation unit housing 50 to the electric circuitboard 51 so that the engine vibrations that reach the electric circuitboard 51 are dampened in their strength, thus permanently reducing themechanical stress of the components involved in signal transmission ofthe piezoelectric pressure sensor 1 in the region of the electriccircuit board 51.

As shown schematically in FIG. 17 for example, a rear area of the sensorflange 20.2 is mechanically connected to a front edge of the evaluationunit housing 50 around its entire perimeter. This mechanical connectiondesirably is carried out by material bonding such as welding, diffusionwelding, thermo compression bonding, soldering, etc. As shown in FIGS.12 and 13 for example, a rear area of the sensor flange 20.2 includes asensor housing frame 20.3. Preferably, the sensor flange 20.2 and thesensor housing frame 20.3 are integrally formed, and as shown in FIGS.12 and 13 for example, the sensor housing frame 20.3 desirably includesat least one strut 20.4 that is oriented parallel to the longitudinalaxis CC′.

As shown in FIGS. 10 and 11 for example, the sensor housing frame 20.3desirably includes two struts 20.4, and the front end of the electriccircuit board 51 is mechanically connected to the two struts 20.4, sothat if one of these connections should fail due to vibration, then theother connection remains fully functional, thereby providing redundancy.Moreover, each of these mechanical connections desirably is made by formclosure wherein each strut 20.4 defines an internal thread that receivesa screw 20.5 attaching the electric circuit board 51 with the strut20.4. This mechanical connection also is an electrical connection, andthe screw 20.5 is mechanically connected to the electric circuit board51 through at least one washer 20.6 that forms an electrical contactbetween the strut 20.4, the screw 20.5 and at least one electricalsignal conductor of the electric circuit board 51. Accordingly, thewasher 20.6 and the screw 20.5 are made of electrically conductivematerial such as pure metals, nickel alloys, cobalt alloys, iron alloys,etc. The electrical connection via the two struts 20.4 is also therebyredundant so that if one of the electrical connections via one of thetwo struts 20.4 should fail, then the other electrical connection viathe other one of the two struts 20.4 remains fully functional. Signalsfrom the return line that are received from the sensor flange 20.2 aretransmitted via the sensor housing frame 20.3 to an electrical signalconductor of the electric circuit board 51. The signal transmission ofthe signals from the return line between the sensor flange 20.2 and theevaluation unit 5 desirably occurs only by means of material bonding andforce closure. The force closure between the struts 20.4 and theelectric circuit board 51 by means of screws 20.5 and washers 20.6dampens mechanical resonance vibrations originating from enginevibrations along the longitudinal axis CC′.

Accordingly, a front area of the signal cable flange 54 desirablyincludes at least one strut 20.4. Preferably, the front area of thesignal cable flange 54 includes two struts 20.4. A rear end of theelectric circuit board 51 desirably is mechanically connected to each ofthe struts 20.4 of the signal cable flange 54. Also in this case, themechanical connection is preferably carried out by force closure whereina screw 20.5 is used to connect the electric circuit board 51 to thestrut 20.4 via a threaded hole defined in the strut 20.4.

FIGS. 12, 13, 15 and 16 schematically show steps of the process ofmanufacturing the piezoelectric pressure sensor 1. The sensor assembly 2according to FIG. 3 and the evaluation unit 5 desirably are manufacturedas separate semi-finished products. This has the advantage thatvariations of the sensor assembly 2 may be produced and combinedinterchangeably with variations of the evaluation unit 5 to formdifferent versions of a piezoelectric pressure sensor 1, the productionof which being cost-effective. Variations of the sensor assembly 2include membranes 21 with different membrane thicknesses and/orpiezoelectric sensors 22 with different operating temperature ranges.Variations of the evaluation unit 5 include electric circuit boards 51with different operating temperature ranges, and/or different signaltypes such as electrically unamplified electrical polarization charges,electrically amplified electric polarization charges, electric voltages,etc.

The sensor assembly 2 includes the membrane 21 accommodated in thesensor housing assembly 20, the piezoelectric sensor 22, the electrodearrangement 23, and the electric insulation body 25. The evaluation unit5 includes the evaluation unit housing 50, the electric circuit board51, the reinforcement element 52.1, 52.2, the electrical connectionelement 53, the signal cable flange 54 and the signal cable 55. Thesignal cable 55 is connected to the evaluation unit 5 via the signalcable flange 54. Aware of the present invention, those skilled in theart also can connect the signal cable to the evaluation unit with anelectrical plug connector such as a signal cable plug etc., instead of asignal cable flange.

In one of the initial steps of the process of manufacturing thepiezoelectric pressure sensor 1, the charge output 23.2 and theelectrical connection element 53 are joined to each other. For thispurpose, the rear end of the charge output 23.2 is pushed into theelectrical connecting element 43 on the longitudinal axis CC′ so thatthe rear end of the charge output 23.2 protrudes into the electricalconnecting element 43 and the outer surface of the charge output 23.2relative to longitudinal axis CC′ and the inner surface of theelectrical connecting element 43 relative to longitudinal axis CC′ arein mechanical contact to each other in certain areas.

In another step of the process of manufacturing the piezoelectricpressure sensor 1, the front end of the electric circuit board 51 ismechanically connected to the sensor housing frame 20.3 by force closurewherein screws threaded into the internal threads defined in the strutsof the sensor housing frame 20.3 mechanically and electrically connectthe electric circuit board 51 to the sensor housing frame 20.3.

In a subsequent process step of manufacturing the piezoelectric pressuresensor 1, the reinforcement element 52.1, 52.2 is mechanically connectedby form closure or force closure to the electric circuit board 51 orthey are interconnected. This form closure or force closure isrepresented schematically in FIGS. 12 and 13. Preferably, severallocking elements 52.3, 52.3′ of one reinforcement element 52.1, 52.2 areengaged in corresponding openings of the other reinforcement element52.1, 52.2 and reinforce the electric circuit board 51 mechanicallyagainst bending loads along the longitudinal axis CC′ and/or along thehorizontal axis BB′.

Referring to FIG. 15, in a further step of the process of manufacturingthe piezoelectric pressure sensor 1, the evaluation unit housing 50 ismoved along the longitudinal axis CC′ toward the sensor flange 20.2. Ineffecting this relative movement, the reinforcement element 52.1, 52.2is at the same time pressed in an interference fit onto the electriccircuit board 51 by the evaluation unit housing 50. This interferencefit between the reinforcement element 52.1, 52.2 and the electriccircuit board 51 mechanically reinforces the electric circuit board 51additionally against bending loads along the longitudinal axis CC′and/or along the horizontal axis BB′.

Subsequently, in another step of the process of manufacturing thepiezoelectric pressure sensor 1, the outer surface of the charge output23.2 and the inner surface of the electrical connection element 53 areelectrically and mechanically connected to each other in certain areas.The electrical and mechanical connection desirably is achieved bymaterial bonding such as welding, diffusion welding, thermo compressionbonding, soldering, etc. A joining tool inserted through the window 52.4of the reinforcement element 52.1, 52.2 desirably carries out thismaterial bonding between the charge output 23.2 and the electricalconnection element 53. The joining tool is not schematically depicted inFIG. 15. Nonetheless, the joining tool desirably can include electrodesof an electrical resistance welding system. Such joining tool desirablyalso can be a crimping tool, a laser, etc. Thus, to enable the joiningtool to perform the material bonding through the window 52.4 of thereinforcement element 52.1 52.2, during this step the evaluation unithousing 50 is spaced apart from the sensor flange 20.2 on longitudinalaxis CC′.

In yet another step of the process of manufacturing the piezoelectricpressure sensor 1, the evaluation unit housing 50 is displacedcompletely relative to the sensor flange 20.2 along the longitudinalaxis CC′ so that, as shown in FIG. 16 for example, the front edge of theevaluation unit housing 50 is in mechanical contact with the rear edgeof the sensor flange 20.2 and is accessible from the outside. Thisdisplacing of the evaluation unit housing 50 is schematically shown inFIG. 16 by an arrow. In this way, the rear area of the sensor flange20.2 is generally flush with the front edge of the evaluation unithousing 50 and is accessible from the outside while the reinforcementelement 52.1, 52.2 is now concealed.

In a following step of the process of manufacturing the piezoelectricpressure sensor 1, the evaluation unit housing 50 is connected to thesensor flange 20.2 in certain areas. Preferably, the front edge of theevaluation unit housing 50 is mechanically connected to the rear edge ofthe sensor flange 20.2 around its entire perimeter. The mechanicalconnection desirably is carried out by material bonding such as welding,diffusion welding, thermo compression bonding, soldering, etc. A joiningtool desirably produces the material bond between the front edge of theevaluation unit housing 50 and the rear edge of the sensor flange 20.2.However, such joining tool is not schematically depicted in FIG. 16.

In yet another step of the process of manufacturing the piezoelectricpressure sensor 1, the evaluation unit housing 50 is mechanicallyconnected to the signal cable flange 54 in certain areas. Preferably,the rear area of the evaluation unit housing 50 is mechanicallyconnected to a front edge of the signal cable flange 54 around itsentire perimeter. This mechanical connection desirably is carried out bymaterial bonding such as welding, diffusion welding, thermo compressionbonding, soldering, etc. A joining tool (not shown) desirably producesthis material bond between the rear area of the evaluation unit housing50 and the front edge of the signal cable flange 54.

Knowing the present invention, those skilled in the art can implement apiezoelectric pressure sensor 1 in which all components of thepiezoelectric pressure sensor 1 that are directly involved in signaltransmission are connected to each other through material bonding.Furthermore, a piezoelectric pressure sensor 1 can be implemented inwhich all mechanical connections between its constituent parts arematerial bonds.

LIST OF REFERENCE NUMERALS

-   -   A, B, C enlarged area    -   AA′, BB′, CC′ axis    -   AB radial plane    -   1 pressure sensor    -   2 sensor assembly    -   5 evaluation unit    -   20 sensor housing assembly    -   20.1 sealing cone    -   20.2 sensor flange    -   20.3 sensor housing frame    -   20.4 struts    -   20.5 screws    -   20.6 washers    -   21 membrane    -   22 sensor    -   22.1, 22.3 support element    -   22.2 piezoelectric sensor element    -   23 electrode arrangement    -   23.1 charge pick-off    -   23.2 charge output    -   25 electric insulation body    -   26 compensation element    -   50 evaluation unit housing    -   51 electric circuit board    -   51.1 high temperature region    -   51.2 normal temperature region    -   52.1, 52.2 reinforcement element    -   52.3, 52.3′ locking element    -   52.4 window    -   52.5 bending zone    -   52.6, 52.6′, 52.6″ area    -   53 electrical connection element    -   53.0 adapter in the form of a socket    -   53.1 annular adapter    -   53.2 compensation element    -   54 signal cable flange    -   55 signal cable

1. A pressure sensor comprising: a sensor assembly that includes anelectrode arrangement and a sensor; which generates signals under theaction of a pressure profile; an evaluation unit that is electricallyconnected to the electrode arrangement to receive the signalstransmitted from the electrode arrangement; and wherein: the evaluationunit includes an evaluation unit housing, an electric circuit board anda reinforcement element, which is arranged in a radial plane between theelectric circuit board and the evaluation unit housing and ismechanically connected to the electric circuit board so as to dampenmechanical resonance vibrations of the electric circuit board that occurin the radial plane.
 2. The pressure sensor according to claim 1,wherein: the sensor is a piezoelectric sensor that producespiezoelectric charges under the action of a pressure profile; and thepiezoelectric charges produced from the piezoelectric sensor arereceived by the electrode arrangement and transmitted as signals to theevaluation unit.
 3. The pressure sensor according to claim 1, wherein:the reinforcement element is arranged around the electric circuit boardin certain areas in the radial plane; and the reinforcement elementencloses the electric circuit board by means of a liner.
 4. The pressuresensor according to claim 1, wherein: the reinforcement element isarranged around the electric circuit board in certain areas in theradial plane; and the reinforcement element encloses the electriccircuit board by means of surface contact.
 5. The pressure sensoraccording to claim 1, wherein the reinforcement element encloses theelectric circuit board in certain areas along a longitudinal axis thatis normal to the radial plane.
 6. The pressure sensor according to claim1, wherein the reinforcement element completely encloses the electriccircuit board in the radial plane.
 7. The pressure sensor according toclaim 1, wherein the reinforcement element fixes the electric circuitboard's freedom of movement in the radial plane relative to theevaluation unit housing.
 8. The pressure sensor according to claim 1,wherein the reinforcement element includes at least two identical shellsthat are mechanically connected to each other and mechanically connectedto the electric circuit board.
 9. The pressure sensor according to claim1, wherein the reinforcement element includes at least two identicalshells that are mechanically connected to each other.
 10. The pressuresensor according to claim 8, wherein: each of the shells is mechanicallyconnected to the electric circuit board via at least one protrudinglocking element; the locking element of one of the shells engages theelectric circuit board through a corresponding opening of the othershell; and the electric circuit board is arranged in the radial planebetween the shells.
 11. The pressure sensor according to claim 8,wherein: the shells are mechanically connected to each other via atleast one protruding locking element; he locking element of one of theshells engages a corresponding opening of the other shell; and theelectric circuit board is arranged in the radial plane between theshells.
 12. The pressure sensor according to claim 1, wherein: theevaluation unit includes an evaluation unit housing; and the evaluationunit housing presses the reinforcement element onto the electric circuitboard in certain areas.
 13. The pressure sensor according to claim 12,wherein: the reinforcement element dudes several sections in alongitudinal direction; and each of the sections has a length along thelongitudinal direction that is at least one of the following lengths: 30mm, 60 mm, and 90 mm.
 14. The pressure sensor according to claim 12,wherein: the evaluation unit housing is configured so that it isslidable over the reinforcement element along the longitudinal directionfrom a rear section of the reinforcement element to a front section ofthe reinforcement element; and the outer diameter of the rear section ofthe reinforcement element is different than the outer diameter of thefront section of the reinforcement element.
 15. The pressure sensoraccording to claim 12, wherein: the evaluation unit housing is slidableover the reinforcement element along the longitudinal direction from arear section of the reinforcement element to a central section of thereinforcement element and from the central section to a front section;the reinforcement element has a different outer diameter in each of therear section, the central section and the front section; the outerdiameter of the central section of the reinforcement element is slightlyoversized as compared to the inner diameter of the evaluation unithousing; and notwithstanding the slight oversize of the outer diameterof the central section of the reinforcement element relative to theinner diameter of the evaluation unit housing, the evaluation unithousing 50 is manually slidable over the central section of thereinforcement element.
 16. The pressure sensor according to claim 14,wherein an outer diameter of the front section of the reinforcementelement has a larger oversize as compared to the inner diameter of theevaluation unit housing such that the evaluation unit housing is notmanually slidable over the reinforcement element.
 17. The pressuresensor according to claim 1, wherein the reinforcement element includesat least one bending zone that is configured and disposed to compensateat least partially for differences in the thermal coefficients of linearexpansion between the reinforcement element and the electric circuitboard.
 18. The pressure sensor according to claim 1, wherein thereinforcement element includes at least one bending zone that isconfigured and disposed to compensate at least partially for differencesin the thermal coefficients of linear expansion between thereinforcement element and the evaluation unit housing.
 19. The pressuresensor according to claim 1, wherein the reinforcement element includesat least one bending zone that is configured and disposed to compensateat least partially for differences in the thermal coefficients of linearexpansion between the electric circuit board and the evaluation unithousing.